The present invention relates to an electro-optical display containing an electrochromic material held in two electrode carrying support plates to manifest reversible variations in the light absorption properties upon application of properly controlled voltage or current. This display is referred to as an "electrochromic display (ECD)" hereinafter.
The present invention relates, more particularly, to lead-in electrode structures connected to segment electrodes in the electrochromic display (ECD) of the segmented type.
A scheme of ECD is as follows. There are two types of electrochromic displays. The first type of ECD utilizes an electrically-induced chemical reduction of a colorless liquid to produce a colored, insoluble film on a cathode surface. In the second type of ECD, the color variation is produced by the change in the opacity of an inorganic solid film formed on electrodes.
A typical colorless liquid suited for the first type of ECD is an aqueous solution of the conducting salt, KBr and an electrochromic material, viologen, which produces a purplish film upon electrochemical reduction. See, for example, C. J. Shoot et al, Appl. Phys. Lett. 23 64 (1973).
The inorganic film used in the second type of ECD is the film of the transition metal oxide material such as tungsten oxide (WO.sub.3). Such a film cooperates with an electrolyte. A typical system of the second type ECD is disclosed in B. W. Faughnan et al, RCA Review 36 177 (1975).
In the above-mentioned types of ECD, a very large current flows through the cell. Therefore, a considerably large voltage reduction occurs upon current flow through the cell at lead-in electrodes connected to segment electrodes. This will create variations of the degree of the coloration among the respective segment electrodes.
Accordingly, an object of the present invention is to enhance the visibility in an electrochromic display of the segmented type.
Another object of the present invention is to stabilize the degree of the coloration of respective display segments included within an electrochromic display of the segmented type.
Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
To achieve the above objects, pursuant to an embodiment of the present invention, lead-in electrodes connected to the respective display segments are shaped in such a manner as to have resistance values inversely proportional to the size of the corresponding display segments. Accordingly, the voltage reductions at the respective display segments are identical with each other even though the sizes of the respective display segments are different from each other.